Windows including glass substrates with solar control coatings provided thereon are known in the art. Such windows may be used in the context of architectural windows, insulating glass (IG) window units, automotive windows, and/or the like.
U.S. Pat. No. 5,514,476 discloses a coated article having a layer stack of glass/SiN/NiCr/Ag/NiCr/SiN, where SiN stands for silicon nitride. While such coatings are certainly good overall coatings usable in applications such as windshields and architectural windows, they tend to be problematic in certain respects. For example, while such layer stacks with NiCr contact layers (a “contact layer” is a layer which contacts an IR reflecting layer such as silver) provide efficient solar control and are overall good coatings, the NiCr (or NiCrNx) layers are lacking in terms of chemical durability. For instance, NiCr is susceptible to significant damage when exposed to acid such as HCl.
It is also known in the art to use niobium (Nb) as a material for contact layers. For example, U.S. Pat. No. 6,355,334 discloses the use of Nb as a contact layer to be provided immediately above a silver layer. U.S. Pat. No. 6,045,896 also discloses the use of Nb as a contact layer immediately above a silver layer. Unfortunately, Nb layers are also lacking with respect to chemical durability. In particular, Nb suffers damage when exposed to certain chemicals such as alkaline solutions, e.g., upon exposure to a one hour NaOH boil test for measuring durability. In commercial use, pinholes can form in dielectric layer(s) thereby exposing the contact layer(s) in certain areas; and if it is damaged by alkaline solutions this can lead to durability issues and coating failure. For example, certain photographs in U.S. patent application Ser. No. 10/370,060, filed Feb. 21, 2003 (hereby incorporated herein by reference) illustrate that Nb layers are often damaged by the one hour NaOH boil test (one hour boil in solution including about 0.1 normal NaOH solution −0.4% NaOH mixed with water—at about 195 degrees F.). For the boil test, see ASTM D 1308-87, incorporated herein by reference.
U.S. Pat. No. 5,837,361 discloses the use of a “sacrificial” alloy of NbCr immediately above a silver layer; where the purpose of the sacrificial layer is to protect the silver from oxidation during deposition of a subsequent metal oxide layer (see the third column, lines fifty to sixty-one). NbCr is a durable material. However, as explained in the '361 patent, this layer is either partially or completely oxidized after the metal oxide layer immediate over it has been deposited. Unfortunately, this oxidation of the NbCr alloy layer can cause the ΔE* value of the coated article to be unduly high if and when heat treatment occurs. For a general description of what is meant by ΔE* values, see U.S. Pat. No. 6,475,626, the disclosure of which is hereby incorporated herein by reference.
Accordingly, there exists a need in the art for a coated article that has improved durability and/or good ΔE* values upon heat treatment. A non-limiting example of improved durability may be achieved by a contact or barrier layer which realizes improved resistance to alkaline solutions (e.g., compared to Nb) and/or acid such as HCl (e.g., compared to NiCr) thereby indicating improved chemical durability. It is an example purpose of certain embodiments of this invention to fulfill this need, and/or other needs which will become apparent to the skilled artisan once given the following disclosure.